This invention relates to a process for preparing 2-alkoxyphenols from alkyl-1,3 benzodioxoles. In particular, it relates to a process for the selective reductive hydrogenolysis of a 2,2-dialkyl-1,3-benzodioxole employing a hydride reducing agent to form a 2-isoalkoxyphenol.
A class of intermediate compounds which has received industry wide attention are the 2-alkoxyphenols. Such compounds are useful, for example, in the preparation of insecticides. In particular, 2-isopropoxyphenol is a key intermediate in the preparation of the insecticide, 2-isopropoxy-1-phenoxy-N-methylcarbonamide.
Traditional methods for synthesizing 2-alkoxyphenols utilized the direct alkylation of catechol with a secondary halide, such as 2-bromopropane or 2-chloropropane. However, this reaction is undesirable for industrial purposes, due to the relatively low halide reactivity and the susceptibility of the catechol to dialkylation, rather than monoalkylation. In general, yields less than 30% of the theoretical amount are obtained employing direct alkylation with secondary halides.
It is known that in the presence of acidic agents, the compound lithium aluminium hydride reductively cleaves certain alicyclic acetals and ketals, known as 1,3-dioxolanes and 1,3-dioxanes, to their corresponding hydroxy ethers, B. Leggetter et al., Can. J. Chem. 43, 1030 (1964); Can. J. Chem 42, 990 (1964); Can. J. Chem. 42 1005 (1964): E. Eliel et al., J. Am. Chem. Soc. 84, 2371 (1962); J. Org. Chem. 30, 2441 (1965) and J. Am. Chem. Soc., 84, 2377 (1962). It is also known that the catalytic hydrogenation of certain acidified alkyl and cycloalkyl ketals provides saturated ether alcohols, Howard et al., J. Org. Chem. 26, 1026 (1959).
However, such reductive cleavage or catalytic hydrogenation has not heretofore been applied to benzodioxoles to selectively produce alkoxyphenols. It has been recognized in the art that benzodioxoles are particularly stable to acids and bases. Accordingly, it was not expected that benzodioxoles would be susceptible to a selective reductive hydrogenolysis to provide an etherified phenol. Attempts to ring-open benzodioxoles and to selectively catalytically hydrogenate them to produce an etherified phenol have been unsuccessful. It has been found that in the case of benzodioxoles, both C-O bonds are cleaved, but the molecule is very resistant to hydrogenolysis, R. T. Arnold et al., J. Am. Chem. Soc., 64, 1410 (1942).
It is accordingly, an object of this invention to provide a process for selectively ring-opening and hydrogenating an alkyl substituted, 1,3-benzodioxole to produce high yields of a 2-alkoxyphenol.